1. Technical Field
This invention relates to the manufacture of circuit boards, more particularly, for a method and apparatus for automatic verification of solder joints of thru-hole mounted electronic components.
2. Background Art
The technological advances made in semiconductor processing has increased the density of electronic components in printed circuit boards. This has led to the predominance of surface mounted devices in printed circuit boards. For various reasons, certain devices do not lend themselves to surface mount technology. Examples of such devices include thru-hole components such as connectors, resistors, switches, and LEDs. This has led to the practice of utilizing thru-hole components in combination with surface mounted devices.
However, this combined technology circuit board presents additional problems. First, the thru-hole components are often manually soldered to the printed circuit board which makes their mechanical and electrical connections susceptible to error. Occasionally, joints are left unsoldered which may be difficult or impossible to detect. For example, an unsoldered connector lead that has a loose mechanical fit can provide an electrical connection under certain conditions and none at other times. This error may be difficult to detect since an intermittent electrical connection may be present when the component's functionality is tested.
Second, automatic testing techniques typically test the electronic functionality of the component. Automatic testing techniques are more desirable since they are faster than manual testing techniques, more efficient, and thereby cost effective. Thru-hole components on a surface mounted circuit board cannot fully utilize this type of testing since it requires verifying the solder connection of each lead in addition to the electrical connection. This is not performed since there is no mechanism which can test the solder connection of each lead in an automated manner.
This problem is illustrated by the prior art printed circuit board configurations shown in FIGS. 3 and 4. FIG. 3 illustrates the reverse side of a typical printed circuit board and FIG. 4 illustrates the corresponding opposite component side. Referring to FIGS. 3 and 4, the printed circuit board 14 has thru-holes, 10a through 10h, used to mount thru-hole components. These components are assembled onto the board by inserting the component leads into the thru-holes which extend from the component side of the board through to the reverse side. The leads are mechanically and electrically connected to the circuit board by individually soldering each lead projecting through its designated thru-hole with solder fill such as electronic tin/lead solder. As this process is performed individually, the reliability that each lead has been soldered is low.
The board contains various test pads 12a thru 12f which provide an automated means for testing electrical connections between various devices and for testing the component's functionality. However, there is no automated mechanism for testing for the presence of or mechanical stability of the solder joints of the individual connector leads. An unsoldered lead may go undetected if it does not affect the electrical functionality of the tested components at the time it is tested. Accordingly, there exists an improved technique for automatically detecting unsoldered thru-hole component leads.
It is an object of this invention to provide an automatic testing technique for detecting unsoldered thru-hole component leads.
It is a further object of this invention to provide a technique as described above which does not significantly increase the cost of the printed circuit board yet increases the quality assurance of the finished assembly.
It is a further object of this invention to provide a technique as described above which does not affect the existing circuit integrity.
Other general and specific objects and advantages of this invention will be apparent and evident from the accompanying drawings and the following description.